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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
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NASA NTRS1989

Climate and the Earth's Radiation Budget

Data from NASA's Earth Radiation Budget (ERB) Experiment instruments carried by the ERB Satellite and by NOAA-9 and -10 are presently evaluated, with a view to the role played by clouds in the global radiation energy balance. While an individual water droplet scatters 85 percent of incident energy in the forward direction, a cloud of such drops can scatter 75 percent or more of the energy backward. The resulting enhancement of surface-atmosphere albedo reduces the solar radiation absorbed by the atmospheric column. Clouds also significantly enhance the long-wave opacity of the atmosphere; like gaseous absorption, this reduces the radiation emitted to space.

Ramanathan, V.↗
NASA NTRS1984

Radiative forcing of stationary planetary waves

To elucidate the role of solar and long-wave transfers in maintaining stationary planetary waves, the potential vorticity equation appropriate to these disturbances in the middle latitudes of the Northern Hemisphere during winter is solved with realistic radiation physics included in the heating term. A series of model experiments demonstrates the roles of the various optically active constituents in maintaining the stationary planetary waves. Clouds and the net radiative heating tend to amplify stationary planetary wavenumber one by increasing the forcing asymmetry, but destructive interference between radiative heating and other diabatic processes and topography causes the net radiative heating to dampen stationary planetary wavenumber two. In the presence of clouds, water vapor and to a lesser extent carbon dioxide damp the waves by reducing cloud-generated forcing asymmetries, particularly at zonal wavenumber one.

Donner, L. J.↗
NASA NTRS1983

Sound radiation from a vibrating cylinder in flow

An alternative approach to the conventional manner of calculating net power output of a source by integrating the energy flux over a distant control surface is presented. The method gives a means of calculating source radiation by an integral only over the source region and eliminates the need for a possibly difficult flux integration. The radiator chosen here is a finite, open ended, cylindrical shell of negligible thickness in the presence of uniform axial flow. A homogeneous medium without external boundaries is assumed. An integral representation and, in the long wave length approximation, an analytical expression for the power radiated by the vibrating cylinder are obtained. The results show power radiation may be increased or decreased by the presence of flow, depending on the relationship between the wave number of the vibration and the size of the radiator. The result is compared with results for simpler geometries.

Smith, M.↗
NASA NTRS1993

Entropy and climate. I - ERBE observations of the entropy production of the earth

An approximate method for estimating the global distributions of the entropy fluxes flowing through the upper boundary of the climate system is introduced, and an estimate of the entropy exchange between the earth and space and the entropy production of the planet is provided. Entropy fluxes calculated from the Earth Radiation Budget Experiment measurements show how the long-wave entropy flux densities dominate the total entropy fluxes at all latitudes compared with the entropy flux densities associated with reflected sunlight, although the short-wave flux densities are important in the context of clear sky-cloudy sky net entropy flux differences. It is suggested that the entropy production of the planet is both constant for the 36 months of data considered and very near its maximum possible value. The mean value of this production is 0.68 x 10 exp 15 W/K, and the amplitude of the annual cycle is approximately 1 to 2 percent of this value.

Stephens, G. L.↗
NASA NTRS2005

Correlation Between Low Frequency Auroral Kilometric Radiation (AKR) and Auroral Structures

Auroral Kilometric Radiation (AKR) is a radio wave emission that has long been associated with auroral activity. AKR is normally observed in the frequency range from -60 - 600 kHz. Low frequency AKR (or LF-AKR) events are characterized as a rapid extension of AKR related emissions to 30 kHz or lower in frequency for typically much less than 10 minutes. LF-AKR emissions predominantly occur within a frequency range of 20 kHz - 30 kHz, but there are LF-AKR related emissions that reach to a frequency of 5 kHz. This study correlates all instances of LF-AKR events during the first four years of observations from the IMAGE spacecraft's Radio Plasma Imager (WI) instrument with auroral observations from the wideband imaging camera (WIC) onboard IMAGE. The correlation between LF-AKR occurrence and WIC auroral observations shows that in the 295 confirmed cases of LF-AKR emissions, bifurcation of the aurora is seen in 74% of the cases. The bifurcation is seen in the dusk and midnight sectors of the auroral oval, where AKR is believed to be generated. The polarization of these LF-AKR emissions has yet to be identified. Although LF-AKR may not be the only phenomena correlated with bifurcated auroral structures, bifurcation will occur in most instances when LF-AKR is observed. The LF-AKR emissions may be an indicator of specific auroral processes sometimes occurring during storm-time conditions in which field-aligned density cavities extend a distance of perhaps 5-6 RE tailward from the Earth for a period of 10 minutes or less.

Paxamickas, Katherine A.↗
NASA NTRS1976

Radiative transfer within the earth's troposphere and stratosphere - A simplified radiative-convective model

A radiative transfer model of the troposphere and stratosphere is presented which includes both long-wave cooling and solar heating due to H2O, CO2 and O3 and has a simplified formulation which facilitates the inclusion of Doppler broadening, H2O continuum bands, hot and minor isotopic bands of CO2, and overlap of H2O bands with CO2 and O3 bands. The radiative model is used to develop an accurate radiative-convective model for studying the global surface temperature, stratospheric thermal structure and the net outgoing long-wave flux.

Ramanathan, V.↗
NASA NTRS2002

The Surface Energy Budget and Precipitation Efficiency for Convective Systems During TOGA, COARE, GATE, SCSMEX and ARM: Cloud-Resolving Model Simulations

A two-dimensional version of the Goddard Cumulus Ensemble (GCE) Model is used to simulate convective systems that developed in various geographic locations. Observed large-scale advective tendencies for potential temperature, water vapor mixing ratio, and horizontal momentum derived from field campaigns are used as the main forcing. By examining the surface energy budgets, the model results show that the two largest terms are net condensation (heating/drying) and imposed large-scale forcing (cooling/moistening) for tropical oceanic cases. These two terms arc opposite in sign, however. The contributions by net radiation and latent heat flux to the net condensation vary in these tropical cases, however. For cloud systems that developed over the South China Sea and eastern Atlantic, net radiation (cooling) accounts for about 20% or more of the net condensation. However, short-wave heating and long-wave cooling are in balance with each other for cloud systems over the West Pacific region such that the net radiation is very small. This is due to the thick anvil clouds simulated in the cloud systems over the Pacific region. Large-scale cooling exceeds large-scale moistening in the Pacific and Atlantic cases. For cloud systems over the South China Sea, however, there is more large-scale moistening than cooling even though the cloud systems developed in a very moist environment. though For three cloud systems that developed over a mid-latitude continent, the net radiation and sensible and latent heat fluxes play a much more important role. This means the accurate measurement of surface fluxes and radiation is crucial for simulating these mid-latitude cases.

Tao, W.-K.↗
NASA NTRS1983

Nonlinear scattering from a plasma column. I - Theory. II Special cases

The scattered signal excited by nonlinear mixing of two plane waves normally incident on an infinitely long column of plasma is investigated. A general solution is obtained for the polarization in which the electric field vectors of the waves are perpendicular to the column axis and the column is assumed to be radically inhomogeneous. This general theory is then applied to the special cases of the inhomogeneous column in the long-wavelength limit, and the homogeneous column both for the general case and in the long-wavelength limit. It is determined that dipole and quadrupole components should predominate in the polar radiation pattern for the long-wavelength case. The special case of second harmonic generation due to a single incident wave is analyzed in detail. Nonlinear scattering coefficients are computed, and the corresponding polar radiation patterns are determined. The findings of this study are employed to evaluate the feasibility of observing nonlinear scattering from meteor trails.

Crawford, F. W.↗
NASA NTRS2008

A Global Model Simulation of Aerosol Effects of Surface Radiation Budget- Toward Understanding of the "Dimming to Brightening" Transition

We present a global model study on the role aerosols play in the change of solar radiation at Earth's surface that transitioned from a decreasing (dimming) trend to an increasing (brightening) trend. Our primary objective is to understand the relationship between the long-term trends of aerosol emission, atmospheric burden, and surface solar radiation. More specifically, we use the recently compiled comprehensive global emission datasets of aerosols and precursors from fuel combustion, biomass burning, volcanic eruptions and other sources from 1980 to 2006 to simulate long-term variations of aerosol distributions and optical properties, and then calculate the multi-decadal changes of short-wave radiative fluxes at the surface and at the top of the atmosphere by coupling the GOCART model simulated aerosols with the Goddard radiative transfer model. The model results are compared with long-term observational records from ground-based networks and satellite data. We will address the following critical questions: To what extent can the observed surface solar radiation trends, known as the transition from dimming to brightening, be explained by the changes of anthropogenic and natural aerosol loading on global and regional scales? What are the relative contributions of local emission and long-range transport to the surface radiation budget and how do these contributions change with time?

Chin, Mian↗
NASA NTRS1985

The effect of topography on the evolution of unstable disturbances in a baroclinic atmosphere

A two layer spectral quasi-geostrophic model is used to simulate the effects of topography on the equilibria, their stability, and the long term evolution of incipient unstable waves. The flow is forced by latitudinally dependent radiative heating. Dissipation is in the form of Rayleigh friction. An analytical solution is found for the propagating finite amplitude waves which result from baroclinic instability of the zonal winds when topography is absent. The appearance of this solution for wavelengths just longer than the Rossby radius of deformation and disappearance of ultra-long wavelengths is interpreted in terms of the Hopf bifurcation theory. Simple dynamic and thermodynamic criteria for the existence of periodic Rossby solutions are presented. A Floquet stability analysis shows that the waves are neutral. The nature of the form drag instability of high index equilibria is investigated. The proximity of the equilibrium shear to a resonant value is essential for the instability, provided the equilibrium occurs at a slightly stronger shear than resonance.

Clark, J. H. E.↗
NASA NTRS1985

Radiation from long pulse train electron beams in space plasmas

A previous study of electromagnetic radiation from a finite train of electron pulses is extended to an infinite train of such pulses. The electrons are assumed to follow an idealized helical path through a space plasma in such a manner as to retain their respective position within the beam. This leads to radiation by coherent spontaneous emission. The waves of interest in this region are the whistler slow (compressional) and fast (torsional) Alfven waves. Although a general theory is developed, analysis is then restricted to two approximations, the short and long electron beam. Formulas for the radiation per unit solid angle from the short beam are presented as a function of both propagation and ray angles, electron beam pulse width and separation and beam current, voltage, and pitch angle. Similar formulas for the total power radiated from the long beam are derived as a function of frequency, propagation angle, and ray angle. Predictions of the power radiated are presented for representative examples as determined by the long beam theory.

Harker, K. J.↗
NASA NTRS1982

Inhomogeneous cosmology - Gravitational radiation in Bianchi backgrounds

An exact formalism is developed for describing cosmological models with strong, long wavelength gravitational waves of general polarization, propagating over backgrounds corresponding to Bianchi types I through VII. A new metric which exhibits the appropriate symmetries of two equivalent independent polarizations of gravitational waves is introduced and discussed. The formalism is applied to an empty type I cosmology, and it is shown how the original z-dependent chaotic singularity structure transforms itself into gravitational radiation propagating along the z-axis in a Bianchi I background.

Adams, P. J.↗
NASA NTRS2021

Stokes resolved differential temperature: an important metric of polarimetric precision in the long-wave infrared

In remote sensing, radiometric measurements taken in the mid-wave infrared and beyond (λ >3μm) are commonly reported in units of Kelvin by utilizing Planck’s radiation law to relate measured radiance and target brightness temperature (Tb). Thus, it is desirable to match this formalism in thermal polarimetry and report the unnormalized Stokes parameters in units of K instead of radiance (Wm−2sr−1). This approach also al-lows common performance metrics in long-wave infrared (LWIR) imaging such as Noise Equivalent DifferentialTemperature (NEDT) to be modified and extended to metrics of polarimetric accuracy and precision. However, since the relationship between measured radiance and Tb are non-linear, the conversion of I, Q, and U in units of radiance to Tb,Tb,Q, and Tb,U in K is ambiguous. As a solution a metric of performance for thermal linear Stokes polarimetry, the Stokes resolved differential temperature (SRDT), is introduced.

polarimetry↗
NASA NTRS2002

Far-Infrared and Millimeter Continuum Studies of K-Giants: Alpha Boo and Alpha Tau

We have imaged two normal, non-coronal, infrared-bright K-giants, alpha Boo and alpha Tau, in the 1.4-millimeter and 2.8-millimeter continuum using BIMA. These stars have been used as important absolute calibrators for several infrared satellites. Our goals are: (1) to probe the structure of their upper photospheres; (2) to establish whether these stars radiate as simple photospheres or possess long-wavelength chromospheres; and (3) to make a connection between millimeter-wave and far-infrared absolute flux calibrations. To accomplish these goals we also present ISO Long Wavelength Spectrometer (LWS) measurements of both these K-giants. The far-infrared and millimeter continuum radiation is produced in the vicinity of the temperature minimum in a Boo and a Tau, offering a direct test of the model photospheres and chromospheres for these two cool giants. We find that current photospheric models predict fluxes in reasonable agreement with those observed for those wavelengths which sample the upper photosphere, namely less than or equal to 170 micrometers in alpha Tau and less than or equal to 125 micrometers in alpha Boo. It is possible that alpha Tau is still radiative as far as 0.9 - 1.4 millimeters. We detect chromospheric radiation from both stars by 2.8 millimeters (by 1.4 millimeters in alpha Boo), and are able to establish useful bounds on the location of the temperature minimum. An attempt to interpret the chromospheric fluxes using the two-component "bifurcation model" proposed by Wiedemann et al. (1994) appears to lead to a significant contradiction.

Cohen, Martin↗
NASA NTRS1984

The acoustic radiation force on a heated (or cooled) rigid sphere - Theory

A finite amplitude sound wave can exert a radiation force on an object due to second-order effect of the wave field. The radiation force on a rigid small sphere (i.e., in the long wavelength limit), which has a temperature different from that of the environment, is presently studied. This investigation assumes no thermally induced convection and is relevant to material processing in the absence of gravity. Both isotropic and nonisotropic temperature profiles are considered. In this calculation, the acoustic effect and heat transfer process are essentially decoupled because of the long wavelength limit. The heat transfer information required for determining the force is contained in the parameters, which are integrals over the temperature distribution.

Lee, C. P.↗
NASA NTRS2010

Response of the Water Cycle of West Africa and Atlantic to Radiative Forcing by Saharan Dust

The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence in support of the "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feed back triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Easter Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean. region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while long wave has the opposite response. The elevated dust layer warms the air over Nest Africa and the eastern Atlantic. The condensation heating associated with the induced deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface energy fluxes, resulting in cooling of the Nest African land and the eastern Atlantic, and a warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

Lau, K. M.↗